4speedC4

Hey Guys,
I picked up a 1987 manual trans convertible last week, 42k miles. The only issue it has is it rarely idles smoothly and consistently, sometimes it will refuse to idle and die every time the clutch is pushed, other times it will surge between 700-1200 rpm. According to receipts that came with the car, in the last ten years and about 10k miles the MAF, ignition module, head gasket, plugs, wires, cap and rotor were all changed, along with two ECM replacements. I set base timing today at 6 degrees BTDC and noticed that while the check engine light came on for code 42 like its supposed to, it then went away without disconnecting the battery. Just wondering what you guys think I should check, this is my first GM product I’ve had to work on so some of the electronics and such are still new to me. I also have an OBD 1 Scanner and took pictures of the data stream when it was idling half decent today just to see if anything seems off to anyone that someone knows what they are looking at lol. Thanks in advance and I look forward to any suggestions.

jv9999

I don't see anything that looks too far off. I would suspect you have a vacuum leak. There are many places for a TPI and intake to leak. The unmeasured air will cause the lean condition and a hunting idle. You can try starting fluid or propane. I like using a trickle from a garden house. You can often hear it suck the water in. You can also consider the IAC (idle air control) if you're sure there are no vacuum leaks. My 2c